argdist for object__alloc probe shows size 0 for class instances.

this is the sample output with command.

./argdist -p 10069 -C "u:$LIBJVM:object__alloc():char*,unsigned int,uintptr_t:arg2,arg3,arg4" -I 5

COUNT EVENT
1 arg2 = Test, arg3 = 4, arg4 = 0
1 arg2 = java/lang/String, arg3 = 16, arg4 = 0
1 arg2 = [B, arg3 = 2, arg4 = 40
4 arg2 = java/nio/HeapCharBuffer, arg3 = 23, arg4 = 0

any idea why size(arg4) is 0 for Test class which I hv instantiated ?